Four p38 MAPK isoforms (alpha, beta, gamma and delta respectively), have been identified each displaying different patterns of tissue expression in man. The p38 MAPK alpha and beta isoforms are found ubiquitously in the body, being present in many different cell types. The alpha isoform is well characterized in terms of its role in inflammation. Although studies using a chemical genetic approach in mice indicate that the p38 MAPK beta isoform does not play a role in inflammation (O'Keefe, S. J. et al., J. Biol. Chem., 2007, 282(48):34663-71.), it may be involved in pain mechanisms through the regulation of COX2 expression (Fitzsimmons, B. L. et al., Neuroreport, 2010, 21(4):313-7). These isoforms are inhibited by a number of previously described small molecular weight compounds. Early classes of inhibitors were highly toxic due to the broad tissue distribution of these isoforms which resulted in multiple off-target effects of the compounds. Furthermore, development of a substantial number of inhibitors has been discontinued due to unacceptable safety profiles in clinical studies (Pettus, L. H. and Wurz, R. P., Curr. Top. Med. Chem., 2008, 8(16):1452-67.). As these adverse effects vary with chemotype, and the compounds have distinct kinase selectivity patterns, the observed toxicities may be structure-related rather than p38 mechanism-based.
Less is known about the p38 MAPK gamma and delta isoforms, which, unlike the alpha and beta isozymes are expressed in specific tissues and cells. The p38 MAPK-delta isoform is expressed more highly in the pancreas, testes, lung, small intestine and the kidney. It is also abundant in macrophages and detectable in neutrophils, CD4+ T cells and in endothelial cells (Shmueli, O. et al., Comptes Rendus Biologies, 2003, 326(10-11):1067-1072; Smith, S. J. Br. J. Pharmacol., 2006, 149:393-404; Hale, K. K., J. Immunol., 1999, 162(7):4246-52; Wang, X. S. et al., J. Biol. Chem., 1997, 272(38):23668-23674.) Very little is known about the distribution of p38 MAPK gamma although it is expressed more highly in brain, skeletal muscle and heart, as well as in lymphocytes and macrophages (Shmueli, O. et al., Comptes Rendus Biologies, 2003, 326(10-11):1067-1072; Hale, K. K., J. Immunol., 1999, 162(7):4246-52; Court, N. W. et al., J. Mol. Cell. Cardiol., 2002, 34(4):413-26; Mertens, S. et al., FEBS Lett., 1996, 383(3):273-6.).
Selective small molecule inhibitors of p38 MAPK gamma and p38 MAPK delta are not currently available, although one previously disclosed compound, BIRB 796, is known to possess pan-isoform inhibitory activity. The inhibition of p38 MAPK gamma and delta isoforms is observed at higher concentrations of the compound than those required to inhibit p38 MAPK alpha and p38 beta (Kuma, Y., J. Biol. Chem., 2005, 280:19472-19479.). In addition BIRB 796 also impaired the phosphorylation of p38 MAPKs or JNKs by the upstream kinase MKK6 or MKK4. Kuma discussed the possibility that the conformational change caused by the binding of the inhibitor to the MAPK protein may affect the structure of both its phosphorylation site and the docking site for the upstream activator, thereby impairing the phosphorylation of p38 MAPKs or JNKs.
p38 MAP kinase is believed to play a pivotal role in many of the signalling pathways that are involved in initiating and maintaining chronic, persistent inflammation in human disease, for example, in severe asthma and in COPD (Chung, F., Chest, 2011, 139(6):1470-1479.). There is now an abundant literature which demonstrates that p38 MAP kinase is activated by a range of pro-inflammatory cytokines and that its activation results in the recruitment and release of additional pro-inflammatory cytokines. Indeed, data from some clinical studies demonstrate beneficial changes in disease activity in patients during treatment with p38 MAP kinase inhibitors. For instance Smith describes the inhibitory effect of p38 MAP kinase inhibitors on TNFα (but not IL-8) release from human PBMCs.
The use of inhibitors of p38 MAP kinase in the treatment of chronic obstructive pulmonary disease (COPD) has also been proposed. Small molecule inhibitors targeted to p38 MAPK α/β have proved to be effective in reducing various parameters of inflammation in cells and in tissues obtained from patients with COPD, who are generally corticosteroid insensitive, (Smith, S. J., Br. J. Pharmacol., 2006, 149:393-404.) as well as in various in vivo animal models (Underwood, D. C. et al., Am. J. Physiol., 2000, 279:L895-902; Nath, P. et al., Eur. J. Pharmacol., 2006, 544:160-167.). Irusen and colleagues have also suggested the possible involvement of p38 MAPK α/β with corticosteroid insensitivity via the reduction of binding affinity of the glucocorticoid receptor (GR) in nuclei (Irusen, E. et al., J. Allergy Clin. Immunol., 2002, 109:649-657.). Clinical experience with a range of p38 MAP kinase inhibitors, including AMG548, BIRB 796, VX702, SCI0469 and SCI0323 has been described (Lee, M. R. and Dominguez, C., Current Med. Chem., 2005, 12:2979-2994.).
COPD is a condition in which the underlying inflammation is reported to be substantially resistant to the anti-inflammatory effects of inhaled corticosteroids. Consequently, a superior strategy for treating COPD would be to develop an intervention which has both inherent anti-inflammatory effects and the ability to increase the sensitivity of the lung tissues of COPD patients to inhaled corticosteroids. A recent publication of Mercado (Mercado, N., et al., Mol. Pharmacol., 2011, 80(6):1128-1135.) demonstrates that silencing p38 MAPK γ has the potential to restore sensitivity to corticosteroids. Consequently there may be a dual benefit for patients in the use of a p38 MAP kinase inhibitor for the treatment of COPD and severe asthma. However, the major obstacle hindering the utility of p38 MAP kinase inhibitors in the treatment of human chronic inflammatory diseases has been the severe toxicity observed in patients resulting in the withdrawal from clinical development of many compounds including all those specifically mentioned above.
Many patients diagnosed with asthma or with COPD continue to suffer from uncontrolled symptoms and from exacerbations of their medical condition that can result in hospitalisation. This occurs despite the use of the most advanced, currently available treatment regimens, comprising of combination products of an inhaled corticosteroid and a long acting β-agonist. Data accumulated over the last decade indicates that a failure to manage effectively the underlying inflammatory component of the disease in the lung is the most likely reason that exacerbations occur. Given the established efficacy of corticosteroids as anti-inflammatory agents and, in particular, of inhaled corticosteroids in the treatment of asthma, these findings have provoked intense investigation. Resulting studies have identified that some environmental insults invoke corticosteroid-insensitive inflammatory changes in patients' lungs. An example is the response arising from virally-mediated upper respiratory tract infections (URTI), which have particular significance in increasing morbidity associated with asthma and COPD.
Epidemiological investigations have revealed a strong association between viral infections of the upper respiratory tract and a substantial percentage of the exacerbations suffered by patients already diagnosed with chronic respiratory diseases. Some of the most compelling data in this regard derives from longitudinal studies of children suffering from asthma (Papadopoulos, N. G., Papi, A., Psarras, S. and Johnston, S. L., Paediatr. Respir. Rev., 2004, 5(3):255-260.). A variety of additional studies support the conclusion that a viral infection can precipitate exacerbations and increase disease severity. For example, experimental clinical infections with rhinovirus have been reported to cause bronchial hyper-responsiveness to histamine in asthmatics that is unresponsive to treatment with corticosteroids (Grunberg, K., Sharon, R. F., et al., Am. J. Respir. Crit. Care Med., 2001, 164(10):1816-1822.). Further evidence derives from the association observed between disease exacerbations in patients with cystic fibrosis and HRV infections (Wat, D., Gelder, C., et al., J. Cyst. Fibros., 2008, 7:320-328.). Also consistent with this body of data is the finding that respiratory viral infections, including rhinovirus, represent an independent risk factor that correlates negatively with the 12 month survival rate in paediatric, lung transplant recipients (Liu, M., Worley, S., et al., Transpl. Infect. Dis., 2009, 11(4):304-312.).
Clinical research indicates that the viral load is proportionate to the observed symptoms and complications and, by implication, to the severity of inflammation. For example, following experimental rhinovirus infection, lower respiratory tract symptoms and bronchial hyper-responsiveness correlated significantly with virus load (Message, S. D., Laza-Stanca, V., et al., PNAS, 2008; 105(36):13562-13567.). Similarly, in the absence of other viral agents, rhinovirus infections were commonly associated with lower respiratory tract infections and wheezing, when the viral load was high in immunocompetent paediatric patients (Gerna, G., Piralla, A., et al., J. Med. Virol., 2009, 81(8):1498-1507.).
Interestingly, it has been reported recently that prior exposure to rhinovirus reduced the cytokine responses evoked by bacterial products in human alveolar macrophages (Oliver, B. G., Lim, S., et al., Thorax, 2008, 63:519-525.). Additionally, infection of nasal epithelial cells with rhinovirus has been documented to promote the adhesion of bacteria, including S. aureus and H. influenzae (Wang, J. H., Kwon, H. J. and Yong, J. J., The Laryngoscope, 2009, 119(7):1406-1411.). Such cellular effects may contribute to the increased probability of patients suffering a lower respiratory tract infection following an infection in the upper respiratory tract. Accordingly, it is therapeutically relevant to focus on the ability of novel interventions to decrease viral load in a variety of in vitro systems, as a surrogate predictor of their benefit in a clinical setting.
High risk groups, for whom a rhinovirus infection in the upper respiratory tract can lead to severe secondary complications, are not limited to patients with chronic respiratory disease. They include, for example, the immune compromised who are prone to lower respiratory tract infection, as well as patients undergoing chemotherapy, who face acute, life-threatening fever. It has also been suggested that other chronic diseases, such as diabetes, are associated with a compromised immuno-defence response. This increases both the likelihood of acquiring a respiratory tract infection and of being hospitalised as a result (Peleg, A. Y., Weerarathna, T., et al., Diabetes Metab. Res. Rev., 2007, 23(1):3-13; Kornum, J. B., Reimar, W., et al., Diabetes Care, 2008, 31(8):1541-1545.).
Whilst upper respiratory tract viral infections are a cause of considerable morbidity and mortality in those patients with underlying disease or other risk factors; they also represent a significant healthcare burden in the general population and are a major cause of missed days at school and lost time in the workplace (Rollinger, J. M. and Schmidtke, M., Med. Res. Rev., 2010, Doi 10.1002/med.20176.). These considerations make it clear that novel medicines, that possess improved efficacy over current therapies, are urgently required to prevent and treat rhinovirus-mediated upper respiratory tract infections. In general the strategies adopted for the discovery of improved antiviral agents have targeted various proteins produced by the virus, as the point of therapeutic intervention. However, the wide range of rhinovirus serotypes makes this a particularly challenging approach to pursue and may explain why, at the present time, a medicine for the prophylaxis and treatment of rhinovirus infections has yet to be approved by any regulatory agency.
Viral entry into the host cell is associated with the activation of a number of intracellular signalling pathways which are believed to play a prominent role in the initiation of inflammatory processes (reviewed by Ludwig, S, 2007; Signal Transduction, 7:81-88.) and of viral propagation and subsequent release. One such mechanism, which has been determined to play a role in influenza virus propagation in vitro, is activation of the phosphoinositide 3-kinase/Akt pathway. It has been reported that this signalling pathway is activated by the NS1 protein of the virus (Shin, Y. K., Liu, Q. et al., J. Gen. Virol., 2007, 88:13-18.) and that its inhibition reduces the titres of progeny virus (Ehrhardt, C., Marjuki, H. et al., Cell Microbiol., 2006, 8:1336-1348.).
Furthermore, the MEK inhibitor U0126 has been documented to inhibit viral propagation without eliciting the emergence of resistant variants of the virus (Ludwig, S., Wolff, T. et al., FEBS Lett., 2004, 561(1-3):37-43.). More recently, studies targeting inhibition of Syk kinase have demonstrated that the enzyme plays an important role in mediating rhinovirus entry into cells and also virus-induced inflammatory responses, including ICAM-1 up-regulation (Sanderson, M. P., Lau, C. W. et al., Inflamm. Allergy Drug Targets, 2009, 8:87-95.). Syk activity is reported to be controlled by c-Src as an upstream kinase in HRV infection (Lau, C. et al., J. Immunol., 2008, 180(2):870-880.). A small number of studies have appeared that link the activation of cellular Src (Src1 or p60-Src) or Src family kinases to infection with viruses. These include a report that adenovirus elicits a PI3 kinase mediated activation of Akt through a c-Src dependent mechanism. It has also been suggested that Rhinovirus-39 induced IL-8 production in epithelial cells depends upon Src kinase activation (Bentley, J. K., Newcomb, D. C., J. Virol., 2007, 81:1186-1194.). Finally, it has been proposed that activation of Src kinase is involved in the induction of mucin production by rhinovirus-14 in epithelial cells and sub-mucosal glands (Inoue, D. and Yamaya, M., Respir. Physiol. Neurobiol., 2006, 154(3):484-499.).
It has been disclosed previously that compounds that inhibit the activity of both c-Src and Syk kinases are effective agents against rhinovirus replication (Charron, C. E. et al., WO 2011/158042.) and that compounds that inhibit p59-HCK are effective against influenza virus replication (Charron, C. E. et al., WO 2011/070369.). For the reasons summarised above, compounds designed to treat chronic respiratory diseases that combine these inherent properties with the inhibition of p38 MAPKs, are expected to be particularly efficacious.
Certain p38 MAPK inhibitors have also been described as inhibitors of the replication of respiratory syncitial virus (Cass, L. et al., WO 2011/158039.).
Furthermore, it is noteworthy that a p38 MAPK inhibitor was found to deliver benefit for patients with IBD after one week's treatment which was not sustained over a four week course of treatment (Schreiber, S. et al., Clin. Gastro. Hepatology, 2006, 4:325-334.).
In addition to playing key roles in cell signalling events which control the activity of pro-inflammatory pathways, kinase enzymes are now also recognised to regulate the activity of a range of cellular functions. Among those which have been discussed recently are the maintenance of DNA integrity (Shilo, Y. Nature Reviews Cancer, 2003, 3:155-168.) and co-ordination of the complex processes of cell division. An illustration of recent findings is a publication describing the impact of a set of inhibitors acting upon the so-called “Olaharsky kinases” on the frequency of micronucleus formation in vitro (Olaharsky, A. J. et al., PLoS Comput. Biol., 2009, 5(7):e1000446.). Micronucleus formation is implicated in, or associated with, disruption of mitotic processes and is therefore an undesirable manifestation of potential toxicity. Inhibition of glycogen synthase kinase 3α (GSK3α) was found to be a particularly significant factor that increases the likelihood of a kinase inhibitor promoting micronucleus formation. Recently, inhibition of the kinase GSK3β with RNAi was also reported to promote micronucleus formation (Tighe, A. et al., BMC Cell Biology, 2007, 8:34.).
It may be possible to attenuate the adverse effects arising from drug interactions with Olaharsky kinases, such as GSK3α, by optimisation of the dose and/or by changing the route of administration. However, it would be more advantageous to identify therapeutically useful molecules that demonstrate low or undectable activity against these off-target enzymes and consequently elicit little or no disruption of mitotic processes, as measured in mitosis assays.
It is evident from consideration of the literature cited hereinabove that there remains a need to identify and develop new p38 MAP kinase inhibitors that have improved therapeutic potential over currently available treatments. Desirable compounds are those that exhibit a superior therapeutic index by exerting, at the least, an equally efficacious effect as previous agents but, in one or more respects, are less toxic at the relevant therapeutic dose. An objective of the present invention therefore, is to provide such novel compounds that inhibit the enzyme activity of p38 MAP kinase, for example with certain sub-type specificities, together, preferably, with Syk kinase and tyrosine kinases within the Src family (particularly c-Src) thereby possessing good anti-inflammatory properties, and suitable for use in therapy.
In one or more embodiments of the invention disclosed herein the compounds of formula (I) exhibit a longer duration of action and/or persistence of action in comparison to the previously disclosed allosteric p38 MAP kinase inhibitor BIRB 796 (Pargellis, C. et al., Nature Struct. Biol., 2002, 9(4):268-272.).